As semiconductor technology evolve into sub-micron technology nodes, the on-going device scaling results in decreasing of channel length and channel width which may lead to undesirable phenomena, such as narrow width effect (NWE), which causes a shift in threshold voltage (VT). The NWE phenomena entails a depletion of dopants, such as Boron, in the channel region, resulting in lower than designed VT. The depletion of dopants occurs when dopants in the channel region segregate and/or diffuse away from their implanted location during subsequent long thermal cycles. Thus, the NWE undesirably lowers the device VT and the effect caused by the depletion of dopants is more significant as the width of the channel region decreases. Consequently, performance and reliability of one or more types of devices may degrade. In addition, the anomalous VT shift for small geometry devices makes device tuning and optimization very challenging.
From the foregoing discussion, it is desirable to provide a reliable, simplified and cost-effective solution to overcome the NWE limitation, such as but not limited to those with long thermal cycle processes.